What ages do you guys breed your horses and dogs, and how many times do you breed them? 

Also, if you use the twinning potion breeding boost, can you use it multiple times? Or use the trifecta after they are retired if you already used the twinning potion breeding boost? 

i like everything to age sundays so i do it on the sunday before they retire (usually the sunday they turn 15/20 (dog/horse).

Same as what Lemo said. And I've never bred twins before, since there's not a huge market for backups/other people's lines on here. :(

I'll breed once - Same as Lemo. When the horses turn 20 or dogs turn 15. A lot of people don't use the Twinning until later on in their lines in order to get a high price for a Prized foal. Usually in the Paint/AQH lines but sometimes in others too as long as the parents are well pointed and its a higher Gen. :D